(1) Field of Invention
This invention relates to novel methods for preparing fluorinated organic compounds, and more particularly to methods of producing fluorinated olefins having a fluorine on an unsaturated non-terminal carbon.
(2) Description of Related Art
Hydrofluorocarbons (HFCs), in particular hydrofluoroalkenes such as tetrafluoropropenes (including 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf) and 1,3,3,3-tetrafluoro-1-propene (HFO-1234ze)) have been disclosed to be effective refrigerants, fire extinguishants, heat transfer media, propellants, foaming agents, blowing agents, gaseous dielectrics, sterilant carriers, polymerization media, particulate removal fluids, carrier fluids, buffing abrasive agents, displacement drying agents and power cycle working fluids. Unlike chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), both of which potentially damage the Earth's ozone layer, HFCs do not contain chlorine and, thus, pose no threat to the ozone layer.
Several methods of preparing hydrofluoroalkenes are known. For example, U.S. Pat. No. 4,900,874 (Ihara, et. al) describes a method of making fluorine containing olefins by contacting hydrogen gas with fluorinated alcohols. Although this appears to be a relatively high-yield process, commercial handling of hydrogen gas at high temperature is generally unsafe. Also, the cost of producing hydrogen gas, such as building an on-site hydrogen plant, can be, in many situations, prohibitive.
U.S. Pat. No. 2,931,840 (Marquis) describes a method of making fluorine containing olefins by pyrolysis of methyl chloride and tetrafluoroethylene or chlorodifluoromethane. This process produces a relatively low yield and a very large percentage of unwanted and/or unimportant byproducts.
The preparation of HFO-1234yf from trifluoroacetylacetone and sulfur tetrafluoride has been described. See Banks, et al., Journal of Fluorine Chemistry, Vol. 82, Iss. 2, p. 171-174 (1997). Also, U.S. Pat. No. 5,162,594 (Krespan) discloses a process wherein tetrafluoroethylene is reacted with another fluorinated ethylene in the liquid phase to produce a polyfluoroolefin product.